The present invention concerns an installation for the remote monitoring and control of a plurality of devices by means of contacts whose opened or closed position is monitored and controlled.
The invention may be applied, in particular but not restrictively, to railroad equipment such as switches at a switching station, axle counters, level crossings, or any other devices that must be monitored and/or controlled.
As regards the control of railroad switches, for example, conventional use is made of a number of techniques, of which the oldest, which is still implemented today, is on-site lever-activated control, involving the visual monitoring of the closing of the switches.
Use is also made of another type of mechanical control system, which involves controlling said switches from a switching station by means of cables or rods. Using this principle, position control is no longer effected by direct inspection of the closing of the switches, as in the preceding method, but rather from the switching station where the control position is visually ascertained. Since this position is, again, mechanical, it represents, in the safety mode, the position of the switches.
Next, passing from mechanical to the electric systems, there is another family of installations in which the position of the switches is monitored electrically from a station generally linked to a remote-control system, when the switches to be maneuvered are controlled by motors.
This monitoring system unites data acquisition and transmission. Acquisition generally occurs by closing electrical contacts by means of switches which are connected mechanically by means of a repeating system or after rotational conversion, to the blades of the switches. Transmission is normally occurs by using these electrical contacts to set up or break the flow of current in as many distinct loops as there are contacts to be monitored. The current source is generally placed in the switching station, as is the means for ascertaining the opened or closed state of the loops. For reasons of simplicity, transmission is not multiplexed, so that a minimum of four contacts and five wires are needed if one wishes to have loops capable of detecting individually the closing or unclosing of each of the blades composing the switch. Similarly, the lack of multiplexing prohibits the sharing of the transmission means, which would allow the remote monitoring of several switches.
In practice, the methods listed above entail many problems.
In particular, as regards the mechanical methods, on-site manipulation and control require the presence of a human agent, and thus his movement toward each of the switches, thereby entailing a lack of flexibility and substantial expense. Similarly, as regards the mechanical remote monitoring of the switches, one immediately apparent constraint results from the necessarily limited distance from the switching station to the various switches being monitored. Despite increased flexibility and economy as compared with the preceding system, this system is poorly suited to the merging of several small stations into one larger station.
As for the electric installations, remote-monitoring by means of current loops is very reliable, but transmission is costly and certain acquisition techniques are not feasible. Thus, the cost of transmission results from the fact that a minimum of five wires are required to operate four contacts linked to the blades of a single switch, and that it is not possible to share the use of these wires to operate several adjoining switches or those positioned along the same track. In practice, this individual wire requirement also prohibits the use of a radio link between the switch and either the switching station or, in some cases, a train approaching this station. Transmission by means of current loops prohibits the use of acquisition techniques which utilize current or voltage levels or, yet again, signalling frequencies which require, in practice, local signal shaping.